This description is directed to an electrical selector switch, and more particularly to a make-before-break selector switch suitable for high-voltage applications. For the purpose of this document, high voltage is defined as voltages higher than 1,000 volts.
Selector switches, which may be referred to as sectionalizing or four-position loadbreak switches, are used in high voltage operations to electrically connect one or more power sources to a load circuit. For example, electrical utilities have used selector switches in underground single phase networks and in three-phase commercial and industrial networks. One use of these devices is to switch between alternate power sources to allow, for example, reconfiguration of a power distribution system or use of a temporary power source while a main power source is serviced. The desirability of avoiding interruptions in power to customers when switching between alternate power sources has increased with the increased use of computers and electronics. Even a momentary interruption when switching power to perform routine maintenance on a circuit can create substantial problems in a computer data center, such as causing loss of data, system failures, and computer service outages.
Before the advent and wide-spread use of computing devices, electric customers typically were not adversely affected by a momentary power outage or a fluctuation in supply current. Now, many companies rely on complex computer systems for their day-to-day operations; often with little more than a surge protector to secure their valuable data against power outages or fluctuations. Because of this, many customers are extremely sensitive to any irregularities in their electrical supply.
The power distribution systems used to supply power change as customers"" demands and requirements change. For example, an electric utility providing power to a large office building typically needs to reconfigure the power distribution to and within the office building when customers move, rebuild space, and add secondary or alternate power feeds. Additionally, power distribution systems may be reconfigured to perform routine maintenance or to replace damaged components. Using conventional selector switches, an electric utility must momentarily disconnect power feeds when reconfiguring a power distribution system.
Selector switches typically are composed of several subassemblies. One subassembly is the switch block, which is generally triangular in shape, with a place to mount contacts to each of the corners of the switch. These corners are at 90xc2x0 angles from each other. The block supports all of the structures and maintains required spacing and separation between parts. Fixed contacts are mounted to the switch block at two or all three of the block""s corners. These contacts usually are connected to power lines and/or taps that are connected to radial feeders or directly to electrical distribution devices such as transformers.
Another subassembly is a rotating center shaft to which blades are mounted. Typically, these blades rotate in 90xc2x0 increments as the switch mechanism causes the shaft to rotate. There also may be center hub that mounts to the blade and one of the contact positions on the switch block.
There are several variations of switch that can be made from these components. Two of the more common configurations are known as a xe2x80x9cVxe2x80x9d blade switch and a xe2x80x9cTxe2x80x9d blade switch. For a xe2x80x9cVxe2x80x9d blade switch, the blade has two members of the same length and typically at a 90xc2x0 angle from each other. Two of the contacts that are mounted to the switch block may be connected to a first power source and a second power source. The center hub is connected to a radial feeder or to an electrical distribution device such as a transformer. The hub may also be connected to a third power source or to a tap that carries power to a feeder serving several transformers.
With a xe2x80x9cVxe2x80x9d blade and a center hub, the user has four switch positions available. The first position connects the hub and tap (or line connected to the hub) to the first source of power; the second position connects the two sources to each other and the hub. The third position connects the second line to the hub and the fourth is a completely open configuration with none of the lines connected to any of the other lines.
The xe2x80x9cTxe2x80x9d blade has three members, each typically at a 90xc2x0 angle from each other. The switch configured as a xe2x80x9cTxe2x80x9d has fixed contacts at each of three corners of the switch block. A line or tap may be connected to each of these contacts. With this switch blade configuration, the four positions typically connect 1) the first power source to the tap, 2) both power sources to the tap, 3) the second power source to the tap and 4) the two sources together, with no connection to the tap.
Rotating a handle connected to the mechanism can change the connections. The rotation charges and then releases springs that cause the switch shaft and blades to rotate at a speed independent of the rotating speed of the handle. With a make-before-break-version of the switch, each of the projecting legs is bridged by a perimeter contact tie that connects the end of each leg to the other.
The perimeter electrical contact is sized such that, when the selector switch control is moved from the first position to the second position, the coupling of the first power source electrical contact to the load electrical contact is not broken until the coupling of the second power source electrical contact to the load electrical contact is made. As such, the switch provides make-before-break functionality in that a first connection is not broken until after a second connection has been made.
The blade of the make-before-break selector switch may be in essentially a V-shaped configuration, and may include a second insulated arm connecting the perimeter electrical contact, which may be configured essentially as a quarter-circle arc, to the mounting point. Additionally, the blade may be in an essentially T-shaped configuration that, for example, includes a second insulated arm and a third insulated arm, each connecting the perimeter electrical contact, which may be configured as an essentially half-circle arc, to the mounting point. The blade also could have a single arm that ties the perimeter contact to the hub.
In another general aspect, a make-before-break selector switch assembly for use in high-voltage applications includes a switch casing, a selector switch mechanism and operating handle and electrical contacts (including first, second, and/or third electrical contacts), and a make-before-break selector switch blade component. The switch casing may be submersed in an insulating fluid that may include, for example, base ingredients such as mineral oils or vegetable oils, synthetic fluids such as polyol esters, SF6 gas, and silicone fluids, and mixtures of the same.
The details of one or more implementations are set forth in the accompanying drawings and the descriptions below. Other features will be apparent from the descriptions and drawings, and from the claims.